Rinse and drain the chickpeas and black beans in a colander, then place them in a large mixing bowl.

In a separate bowl, whisk together the olive oil, red wine vinegar, dried oregano, salt, and pepper until emulsified.

Pour the dressing over the beans and gently toss to coat them evenly.

Add the sliced red onion, chopped parsley, and crumbled feta cheese to the salad, and toss gently once more.

Cover the bowl and refrigerate for at least 30 minutes before serving to allow the flavors to meld.